Emitter of semiochemical substances supported on a sepiolite, preparation process and applications

ABSTRACT

The present invention provides an emitter of semiochemical substances that comprising a support and a semiochemical subsistence adsorbed in the same, is characterized in that said support is a sepiolite and in that the retaining force between said sepiolite and said semiochemical substance is regulated in such a way that a controlled emission kinetics of said semiochemical substance is obtained. 
     The process for the manufacture of said emitter comprises the operations of modifying a natural sepiolite and of associating it to a semiochemical substance, in such a way that the same is retained with a force such that the emitter has a controlled release kinetics of the substance. 
     The cited emitter is especially useful in the agricultural sector, for insect plague control in crops.

TECHNICAL FIELD OF THE INVENTION

The present invention fits in the agricultural sector and, inparticular, in the control of insect plagues detrimental to crops.

More specifically, the present invention provides new emitters ofsemiochemical substances, with controlled emitting speed, useful for thecontrol of insect plagues in agricultural crops and the process for thepreparation thereof.

PRIOR ART OF THE INVENTION

Insect plagues cause a drastic reduction of crops and insecticides arethe traditional method to combat them. However, the use of insecticideshas problems such as:

Their toxicity for humans and superior animals, which causes governmentsto impose more restrictive regulators for the use thereof.

The lack of selectivity, that converts into the destruction ofbeneficial insects, or of natural predators of the plague that is to befought

The resistance developed by the insects, which makes it necessary toincrease more and more the dosage to maintain the effectiveness thereof.

All of these problems oblige insecticide manufacturers to dedicate moreand more resources to R+D in order to obtain better products, but theproblem continues to exist.

On its part, society demands respect for the environment but at the sametime it requires quality of the agricultural food products, whichrequires the development of new plague control systems basedenvironmental methods.

It is well known that the communication among insects is basically doneby means of a specific type of substances, called “semiochemicalsubstances” (or simply “semiochemicals”), that their organisms naturallyemit.

The knowledge of said semiochemical substances as well as the knowledgeof the information that the same transmit to the insects permits thedevelopment of environmental methods in order to control the behavior ofthe insects.

In accordance with the above, it is possible to transmit a specificmessage to a specific species of insects, inducing a specific responseby means of the artificial emission of synthetic semiochemicals. Hence,for example, if the message is of attraction, the response of the insectwill be directed towards the emitter.

Taking advantage of this inducing capacity the behavior of insects,techniques that permit the control thereof have been developed.Hereinafter a summary of the most important ones is going to be made:

Control, whose purpose is to prevent the occurrence of plagues, tofollow their development and to confirm their extinction by means of acount of the captures that are produced in traps provided with anemitter of an attracting semiochemical.

Sexual confusion, that seeks to prevent the reproduction of insects bymeans of the emission of amounts of a semiochemical that saturates thereceptor organs of the insect preventing it to find members of its samespecies and of the opposite sex.

Massive captures, that seek to significantly reduce the insectpopulation, by means of captures, in traps, with an attractingsemiochemical. Aside from the attractant, a toxic agent for the insect,a sexual sterilizer, an entomopathogenic microorganism or simply gluewhere the insect is adhered and dies, may also be placed in the traps.

The low toxicity of semiochemicals, their high specificity (generally,their action is directed towards a single species), the difficultoccurrence of resistances and their non-existent polluting impact,represent outstanding advantages in contrast to conventionalinsecticides.

So that the use of these semiochemical substances is effective it isnecessary to have physical supports capable of emitting thesemiochemicals in a controlled manner for a sufficient amount of time,in such a way that a concentration in the air capable of cause thedesired response in the insect in a continued manner is achieved.

The cited supports must comply with a series of requirements so thattheir use is effective:

Provide an adequate emitting speed of the semiochemical.

Permit prolonged duration of the emission

Avoid degradation of the semiochemicals

Not produce contaminating residues

Be economical and allow easy application of the semiochemical

Although there is a large variety of emitting supports on the marketsuch as rubber septa (Aldrich Co., UK; The West Co., Pennsylvania;Arthur H. Thomas Co.; Maavit Products, Tel Aviv, Israel), polyethylenepipes (Shin Etsu Chemical Co., Tokyo, Japan), porous plastic laminates(Hercon Lab. Co., New Jersey, USA); capillary fibers (AlbanyInternational, Massachusetts, USA), microcapsules (ICI Agrochemicals,Berks, UK), none of these emitting supports comply with all the abovementioned requirements.

Therefore, there is still the need of emitters of semiochemicalsubstances with supports that acceptably satisfy said requirements and,precisely, this has been the purpose that the applicant's scientificresearch has sought. This research has allowed the attainment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

Just as it is stated in its title, the present invention refers to newemitters of semiochemical substances with a controlled emitting speed,to a process for the preparation thereof and to the applications thereoffor the control of insect plagues in agriculture.

The emitters of the present invention, that comprise a support and asemiochemical substance adsorbed in the support, are characterized inthat said support is a sepiolite and in that the retaining capacitybetween said sepiolite and said semiochemical substance is regulated insuch a way that a controlled emission kinetics of said semiochemicalsubstance is obtained.

Natural sepiolites are crystalline magnesium silicates. Structurally,they are formed in laminae of silica tetrahedrons connected by Mg²⁺cations, in octahedral coordination (see FIG. 1). The laminae formfibers of a length between 0.5 and 1.5μ and in turn, the fibers areconnected together by means of Si—O—Si bridges and carbonates, formingbeams with a thickness of about 200 Å

The specific surface of natural sepiolite is around 200-300 m²/g, andcan be modified to values between 80 and 600 m²/g (according to theB.E.T. method) by means of adequate treatments, wherein the Si—O—Sibridges are broken.

The size of the channel of natural sepiolite is relatively small andthere is a high polarity inside it, caused by the water fromcrystallization and the end hydroxyl groups.

Due to this, the regular molecules of semiochemicals have difficultiesin entering inside the channels, due to the size thereof and the lack ofpolarity, and consequently, the adsorption to the sepiolite support issuperficial, in most of the cases.

The retaining capacity between the sepiolite and the semiochemical canbe carried out from two aspects:

1.—Modification of the sepiolite

2.—Modification of the degree of compacting between the sepiolite andthe adsorbed semiochemical.

Within the first group of modifications the following ones can bementioned:

Modification of the surface cations of the sepiolite

Modification of the specific surface of the sepiolite

Within the second group of modifications the following ones can bementioned:

Modification of the compacting pressure

Modification of the surface/weight ratio of the finally obtained form

Each one of these modifications will now be analyzed in a more detailedmanner.

1. The modification of the surface cations of the sepiolite allowsmodification of the number of adsorption centers and the retaining forceof the semiochemical on the part of the same. An illustrative example ofthis fact is constituted by the use of different sepiolites modifiedsuperficially wherein a specific percentage of surface octahedralmagnesium has been replaced by mono or bivalent cations of groups IA andIIA or by protons. The modification of the surface cations of thesepiolite can be done by treatment of the natural sepiolite with acids(for example, sulfuric acid) or with bases (for example, sodiumhydroxide).

2. The modification of the specific surface of the sepiolite isespecially interesting, taking into account that the fixation of themolecules of semiochemical molecules to the first adsorption layer ismuch greater than the fixation that is produced in the second andsuccessive layers. Upon increasing the adsorption surface of thesepiolite support, an increase of retention of the semiochemical isproduced.

The modification of the specific surface is carried out by means oftreatments similar to those indicated in item one above. Specificsurface values between 80 and 600 m²/g can be achieved.

3. The modification of the compacting pressure during the manufacturingof the emitter makes it possible to act on the emitting speed. Hence,the greater the pressure at which the sepiolite is compacted with thesemiochemical the greater the retention thereof on the support is, thusreducing the emitting speed. On the contrary, a compacting of bothproducts at a lower pressure increases the emitting speed of thesemiochemical. The range of compacting pressures is preferably between0.1 and 20 T/cm², the pressure being chosen in terms of the needs ofemission of the active substance.

4. The modification of the surface/weight ratio of the finally obtainedemitting product also makes it possible to act on the emitting speed ofthe semiochemical. Hence, upon increasing the surface/weight ratio theemitting speed increases; on the contrary, upon reducing said ratio, theemitting speed reduces.

In accordance with the above, for the preparation of the emitters of thepresent invention one or several gradual modifications of the differentphysico-chemical variables mentioned in the above paragraphs can be madein order to adapt the sepiolite supports to the characteristics of thesemiochemicals and to the specific needs of each emission kinetics forthe treatment sought.

The emitters of the present invention can be prepared by associating thesupport and the semiochemical substance by conventional techniques suchas agglomeration, pressing, drying by pulverization and the like, wherebinding components may or may not be used.

For example, the sepiolitic material can be impregnated, by adding tosaid powdered material a solution of semiochemical substance,trimedlure, in dichloromethane in a proportion of 1-20 ml ofdichloromethane per gram of sepiolite+trimedlure, subsequentlyeliminating the dichloromethane.

The emitter thus obtained may be applied in the form of powder, wettablepowder, granulate, pastilles, or conglomerates with any geometric shapethat is desired. Likewise, they may be applied manually or by using anyconventional mechanical device.

Preferably, the proportion of semiochemical substance/sepiolite isbetween 1 and 800 mg. Of semiochemical substance per gram of sepiolite,the proportion being chosen in terms of the needs of emission.

The emitters of semiochemical substances of the present invention areespecially useful in order to treat insect plagues in the agriculturalsector, either by population control techniques, massive captures,sexual confusion or any other type of attracticide traps, producingsterilizing actions in the insects, insecticides or hormone productioninhibitors, among others.

In accordance with the above, the present invention provides newemitters of semiochemical substances that permit controlled and durableemission of the semiochemicals used in the environmental fight againstagricultural plagues, with noteworthy advantages in comparison to theemitters developed up to now. Among said advantages the following onescan be emphasized:

The adaptation to the emitting needs and to the properties of eachsemiochemical.

The capacity to attain high useful life times

The non-existent pollution that they produce, since due to theirchemical nature, they blend in the agricultural soil

Their ease of application since they can be used in pastille, granulateor powder form.

The possibility of compacting them with different shapes in order toadapt them to any support.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 It is a graph of the chemical structure of natural sepiolite, thedifferent types of atoms are represented with the following symbols:

Silicon: •

Magnesium: ∇

Oxygen:

Hydroxyl • inside a circle

Crystallization water: ⊕

FIG. 2 It is a graph of the influence of the cation on the trimedlureemission kinetics in accordance with Example 1. The different sepiolitesare represented win this figure with the following symbols:

sep Na Mg 25%: ▴

sep Mg: X

sep H Mg 25%: ▪

FIG. 3 It is a graph of the influence of the adsorption layer on thetrimedlure emission kinetics in accordance with Example 2. The differentsepiolites have been represented in this figure with the followingsymbols:

sep H, 2^(nd). layer, 13%: ▪

sep H Mg 25%, 2^(nd). layer 33%: X

FIG. 4 It is a graph of the influence of the compacting pressure on thetrimedlure emission kinetics in accordance with Example 3. The differentpressures are represented in the figure with the following symbols:

Pressure 3.1 T/cm²: ▪

Pressure 10.2 T/cm²: ♦

FIG. 5 It is a comparative graph of the field kinetics of a sepiolite inaccordance with the invention in contrast to a conventional emitteraccording to Example 5. The sepiolite Na Mg has been represented by •and the can by ▪ in this figure.

EMBODIMENTS OF THE INVENTION

Hereinafter several examples are given of the use of sepiolites andmodified sepiolite materials, as a semiochemical support, and theadaptation thereof to predetermined emission kinetics, taking as thestandard semiochemical trimedlure (tert-butyl4-chloro-2-methylcyclohexane-1-carboxylate, attractant of fruit fly,Ceratitis capitata)

The emission kinetics of the trimedlure adsorbed in the differentsepiolitic supports obtained is determined according to the followingmethod:

1.—Impregnation of the sepiolite:

This is done by adding to the powdered sepiolitic material, a solutionof trimedlure in dichloromethane and intense stirring for 1 hour,subsequently eliminating the dichloromethane. The impregnated sepioliticmaterial is homogenized by stirring for half an hour and then it iscompacted in a press forming pastilles.

2.—Aeration and aging:

The pastilles are kept at 25° C. and with controlled aeration for 45days. Periodically the amount of trimedlure that remains in thepastilles is determined, by means of extraction with soxhlet with thesuitable solvent and qualitative gas chromatography. The emitting curvesare drawn and the corresponding kinetics are determined with theobtained data.

The determination of the punctual emitting speed is done by using athermostatted aerator, inside of which the pastille of sepioliticmaterial impregnated with trimedlure is placed periodically. Acontrolled air flow is circulated, with a constant temperature for aspecific amount of time. When it comes out, the air passes through acartridge of adsorbent, generally, a Sep-pak C18, where the trimedlure(TML) is retained. Subsequently the cartridge is removed and the amountof trimedlure emitted for a measured amount of time is determined byquantitative gas-liquid chromatography.

Example 1 Modification of the Surface Cations in Sepiolites forControlled Emission of the Semiochemical Trimedlure

Compared Emitting Supports:

Sepiolite Mg (Natural)

Sepiolite H Mg, 25% H⁺. The octahedral Mg has been partially exchangedby H⁺

Sepiolite Na Mg, 25% Na⁺. The octahedral Mg has been partially exchangedby Na.

Preparation of Sepiolites with Suitable Cations:

Sepiolite H Mg 25% was obtained from natural sepiolite by means oftreatment with 1.3N H₂SO₄, at 50° C., for 30 min. with subsequentfiltering and washing with water. The crystallinity of the sample isconfirmed by X-ray diffraction.

Sepiolite Na Mg 25% was obtained by means of treatment of naturalsepiolite with 1N NaOH, at room temperature, for 15 minutes andtreatment in an autoclave at 200° C. for 6 hours, with subsequentfiltering and washing. The crystallinity of the sample (70%) isdetermined by means of X-ray diffraction.

The kinetics obtained are shown in FIG. 2:(Influence of the cation onthe emission kinetics). The maximum retention (most favorable emissionkinetics) is obtained when the exchange cation is Na⁺. The sepiolite HMg retains less trimedlure than sepiolite Mg. The test is carried outwith an initial load of 140 mg of trimedlure/g of sepiolite andpastilles with a 5 mm Ø, a weight of 0.09 g and compacted with apressure of 10.2 T/cm².

Example 2 Modification of the Adsorption Layer for Controlled Emissionof Trimedlure

For the amount of trimedlure given and using sepiolites with a differentspecific surface, the emitting speed thereof can be controlled, in termsof the percentage of trimedlure adsorbed in the 1^(st). or in the2^(nd). adsorption layer. 420 mg of TML/g of sepiolite are used as theinitial load.

Compared Emitting Supports:

Sepiolite H Mg 25% in H⁺. Specific surface 400 m²/g. Percentage of TMLin the 2^(nd). layer: 33%

Sepiolite H. Specific surface 520 m²/g. Percentage of TML in the 2^(nd).layer: 13%

Preparation of Sepiolites with the Adequate Surface:

Sepiolite H Mg 25% in H is prepared according to the method of the aboveexample. Sepiolite H is prepared like sepiolite H Mg 25% but using 3NH₂SO₄.

The kinetics obtained are shown in FIG. 3: (Influence of the adsorptionlayer on the emission kinetics) The increase of retention is observedthe larger the adsorption surface is and, therefore, the smaller thepercentage of trimedlure absorbed on the second layer. The test iscarried out with an initial load of 420 mg of trimedlure/g of sepioliteand pastilles with a 5 mm Ø, a weight of 0.09 g. In this way, by varyingthe proportion of semiochemical in the 1^(st). and 2^(nd). layer, theemission kinetics can be regulated.

Example 3

Modification of the Compacting Pressure of Sepiolites for ControlledEmission of the Semiochemical Trimedlure

Emitting Supports:

Sepiolite H Mg 25% impregnated with 140 mg of trimedlure and compactedat pressures of 3.1 and 10.2 T/cm². This sepiolite is described inexample 1.

The kinetics obtained are shown in FIG. 4: (Influence of the compactingpressure on the emission kinetics). The increase of retention isobserved when the compacting pressure increases. The test is carried outwith an initial load of 140 mg of trimedlure/g of sepiolite andpastilles with a 5 mm Ø and a weight a 0.09 g. The verification that thekinetics obtained with the sepiolites are adequate and of long durationis observed in the following example.

Example 4 Comparison of the Effectiveness (Number of Captures and UsefulLife Time of the Emitter), in the Emission of Trimedlure, of a ModifiedSepiolite in Contrast to the Traditional Emitter Perforated Container

Compared Emitting Supports:

Sepiolite Na Mg 25%, described above is used. The usual plastic can isused as a reference.

Method of Application:

The sepiolite is loaded with trimedlure and tablets are formed with apressure of 2 T/cm². The initial load of the sepiolite pastilles is 500mg of trimedlure, the pastilles are of 2.9 g; the container is alsoloaded with 500 mg. Yellow delta traps with an exchangeable floorimpregnated with glue are used. The traps are placed in alternatingtrees (10 m of distance between the traps). Periodically captures arecounted and the emitters are collected in order to analyze them in thelaboratory by means of extraction and quantitative gas-liquidchromatography.

The emission kinetics of the compared systems are shown in FIG. 5:(Comparison of the field kinetics in sepiolites Na Mg 25% in comparisonto the perforated can with the trimedlure emission). The most favorablekinetics is observed of the sepiolite Na that captures more flies andthat keeps the activity for a longer period of time. A useful life time(period of effectiveness) of 185 days is obtained for sepiolite Na. Thecontainer is clearly inferior, with a useful life of 132 days.

What is claimed is:
 1. A material for emitting semiochemical substancescomprising a support and a semiochemical substance adsorbed in saidsupport, wherein said support is a modified sepiolite having a retainingcapacity for retaining said semiochemical substance, said retainingcapacity of the modified sepiolite being adjusted in such a way that acontrolled emission kinetics of said semiochemical substance isobtained, said modified sepiolite being at least one of a substitutedsepiolite in which up to 40% of surface octahedral magnesium cations hasbeen substituted by cations selected from metal cations of Group IA andIIA and protons; a surface-modified sepiolite having a specific surfacevalue between 80 and 600 m²/g, said specific surface having beenobtained by a treatment of the sepiolite selected from the group oftreatments with an acid and treatments with a base; a compactedsepiolite having a degree of compaction and which has been compactedtogether with said semiochemical substance according to a compactingpressure between 0.1 and 20t/cm²; a surface/weight-modified sepiolite inwhich a selected surface/weight ratio has been adjusted; aplurally-modified sepiolite having properties of at least two of saidsubstituted sepiolite, said surface-modified sepiolite, said compactedsepiolite and said surface-weight-modified sepiolite.
 2. A materialaccording to claim 1, wherein said substituted sepiolite has beenprepared by treating natural sepiolite with a base.
 3. A materialaccording to claim 1, wherein said substituted sepiolite has beenprepared by treating natural sepiolite with an acid.
 4. A materialaccording to claim 1, wherein said substituted sepiolite has beenprepared by treating natural sepiolite with sulfuric acid.
 5. A materialaccording to claim 1, wherein said substituted sepiolite has beenprepared by treating natural sepiolite with sodium hydroxide.
 6. Amaterial according to claim 1, wherein the surface/weight ratio and thedegree of compactation of the support have been adjusted by compacting.7. A material according to claim 1, wherein the surface/weight ratio ofthe surface-weight modified sepiolite has been adjusted duringpreparation of the support.
 8. A material according to claim 1,comprising 1-800 mg of the semiochemical substance per gram of thesupport.
 9. A material according to claim 1, wherein the semiochemicalsubstance is impregnated in the support.
 10. A material according toclaim 1, wherein the semiochemical substance is trimedlure.
 11. Amaterial according to claim 1, wherein the material is a powder.
 12. Amaterial according to claim 1, wherein the material is a granulate. 13.A material according to claim 1, wherein the material is a tablet.
 14. Aprocess for manufacturing the material of claim 1, said processcomprising the operations of modifying a sepiolite to provide asepiolite support in which a semiochemical substance is adsorbed, insuch a way that the retaining capacity of the sepiolite support permitsa controlled release kinetics of said semiochemical substance, whereinthe sepiolite is treated by at least one of substituting up to 40% ofsurface octahedral magnesium cations of the sepiolite by cationsselected from metal cations of Group IA and IIA and protons, andadsorbing the semiochemical substance into the support; adjusting thespecific surface of the sepiolite by a treatment selected from the groupselected from treatments with an acid and treatment with a base, toobtain a specific surface value between 80 and 600 m²/g, and adsorbingthe semiochemical substance into the support; compacting the sepiolitetogether with said semiochemical substance by applying a compactingpressure between 0.1 and 20t/cm²; and adjusting the surface/weight ratiohas to a selected value surface/weight ratio value, and adsorbing thesemiochemical substance into the support.
 15. A process according toclaim 14, wherein said surface magnesium cations are substituted bytreating natural sepiolite with a base.
 16. A process according to claim14, wherein said surface magnesium cations are substituted by treatingnatural sepiolite with an acid.
 17. A process according to claim 14,wherein said surface magnesium cations are substituted by treatingnatural sepiolite with sulfuric acid.
 18. A process according to claim14, wherein that said surface magnesium cations are substituted bytreating natural sepiolite with sodium hydroxide.
 19. A materialaccording to claim 1, wherein said surface-modified sepiolite has beenprepared by treating natural sepiolite with a base.
 20. A materialaccording to claim 1, wherein said surface-modified sepiolite has beenprepared by treating natural sepiolite with an acid.
 21. A materialaccording to claim 1, wherein said surface-modified sepiolite has beenprepared by treating natural sepiolite with sulfuric acid.
 22. Amaterial according to claim 1, wherein said surface-modified sepiolitehas been prepared by treating natural sepiolite with sodium hydroxide.